using System.Reflection;
using FluentAssertions;
using Xunit;

namespace BucketChain.Test;

public sealed class PersonTests
{
    [Fact]
    public void Construction()
    {
        var person = new Person();

        person.LeftNeighbor.Should().BeNull("not set yet");
        person.RightNeighbor.Should().BeNull("not set yet");
        person.HasBucket.Should().BeFalse("no bucket received yet");
        person.LastStepPerformed.Should().Be(0, "performed in no step yet");
    }

    [Fact]
    public void JoinChain_OneOther_Right()
    {
        var firstPerson = new Person();
        var newPerson = new Person();

        newPerson.JoinChain(firstPerson, true);

        firstPerson.LeftNeighbor.Should().BeNull();
        firstPerson.RightNeighbor.Should().BeSameAs(newPerson, "joined on right side");
        newPerson.LeftNeighbor.Should().BeSameAs(firstPerson);
        newPerson.RightNeighbor.Should().BeNull();
    }

    [Fact]
    public void JoinChain_OneOther_Left()
    {
        var firstPerson = new Person();
        var newPerson = new Person();

        newPerson.JoinChain(firstPerson, false);

        firstPerson.LeftNeighbor.Should().BeSameAs(newPerson, "joined on left side");
        firstPerson.RightNeighbor.Should().BeNull();
        newPerson.LeftNeighbor.Should().BeNull();
        newPerson.RightNeighbor.Should().BeSameAs(firstPerson);
    }

    [Fact]
    public void JoinChain_TwoOthers_Left()
    {
        var (firstPerson, secondPerson) = CreateMinimalChain();
        var newPerson = new Person();

        newPerson.JoinChain(firstPerson, false);

        firstPerson.LeftNeighbor.Should().BeSameAs(newPerson, "joined on left side of first person");
        firstPerson.RightNeighbor.Should().BeSameAs(secondPerson, "unchanged");
        secondPerson.LeftNeighbor.Should().BeSameAs(firstPerson, "unchanged");
        secondPerson.RightNeighbor.Should().BeNull();
        newPerson.LeftNeighbor.Should().BeNull();
        newPerson.RightNeighbor.Should().BeSameAs(firstPerson);
    }

    [Fact]
    public void JoinChain_TwoOthers_Right()
    {
        var (firstPerson, secondPerson) = CreateMinimalChain();
        var newPerson = new Person();

        newPerson.JoinChain(secondPerson, true);

        firstPerson.LeftNeighbor.Should().BeNull();
        firstPerson.RightNeighbor.Should().BeSameAs(secondPerson, "unchanged");
        secondPerson.LeftNeighbor.Should().BeSameAs(firstPerson, "unchanged");
        secondPerson.RightNeighbor.Should().BeSameAs(newPerson, "joined on right side of second person");
        newPerson.LeftNeighbor.Should().BeSameAs(secondPerson);
        newPerson.RightNeighbor.Should().BeNull();
    }

    [Fact]
    public void JoinChain_TwoOthers_Center_Option1()
    {
        var (firstPerson, secondPerson) = CreateMinimalChain();
        var newPerson = new Person();

        newPerson.JoinChain(firstPerson, true);

        firstPerson.LeftNeighbor.Should().BeNull();
        firstPerson.RightNeighbor.Should().BeSameAs(newPerson, "joined on right side of first person");
        secondPerson.LeftNeighbor.Should().BeSameAs(newPerson, "joined on left side of second person");
        secondPerson.RightNeighbor.Should().BeNull();
        newPerson.LeftNeighbor.Should().BeSameAs(firstPerson);
        newPerson.RightNeighbor.Should().BeSameAs(secondPerson);
    }

    [Fact]
    public void JoinChain_TwoOthers_Center_Option2()
    {
        var (firstPerson, secondPerson) = CreateMinimalChain();
        var newPerson = new Person();

        newPerson.JoinChain(secondPerson, false);

        firstPerson.LeftNeighbor.Should().BeNull();
        firstPerson.RightNeighbor.Should().BeSameAs(newPerson, "joined on right side of first person");
        secondPerson.LeftNeighbor.Should().BeSameAs(newPerson, "joined on left side of second person");
        secondPerson.RightNeighbor.Should().BeNull();
        newPerson.LeftNeighbor.Should().BeSameAs(firstPerson);
        newPerson.RightNeighbor.Should().BeSameAs(secondPerson);
    }

    [Fact]
    public void FightFire_Simple()
    {
        const double FireInitialSize = 45.67D;
        const double BucketSize = 2.4D;

        var fire = new Fire(FireInitialSize, default(double));
        var bucket = CreateFilledBucket(BucketSize);
        var person = new Person();
        SetBucket(person, bucket, true);

        person.FightFire(fire);

        fire.FireSize.Should().BeApproximately(FireInitialSize - BucketSize,
            double.Epsilon, "fire shrank by amount of water in the bucket");
        bucket.IsEmpty.Should().BeTrue("bucket content has been used");
    }
    
    [Fact]
    public void FightFire_NoBucket()
    {
        const double FireInitialSize = 45.67D;

        var fire = new Fire(FireInitialSize, default(double));
        var person = new Person();

        person.FightFire(fire);

        fire.FireSize.Should().BeApproximately(FireInitialSize,
            double.Epsilon, "fire size did not change");
    }

    [Fact]
    public void UseWell_ExistingBucket_Forward()
    {
        const double WellInitialFillLevel = 20D;
        const double BucketSize = 1.86D;
        
        var well = new Well(WellInitialFillLevel, default(double));
        var bucket = new Bucket(BucketSize);
        var person = new Person();
        SetBucket(person, bucket, true);
        
        person.UseWell(well, null);

        bucket.IsEmpty.Should().BeFalse("has been filled");
        well.LitersRemaining.Should().BeApproximately(WellInitialFillLevel - BucketSize,
            double.Epsilon, "well level has been reduced by bucket amount");
    }
    
    [Fact]
    public void UseWell_ExistingBucket_Backward()
    {
        const double WellInitialFillLevel = 20D;
        const double BucketSize = 1.86D;
        
        var well = new Well(WellInitialFillLevel, default(double));
        var bucket = new Bucket(BucketSize);
        var person = new Person();
        SetBucket(person, bucket, false);
        
        person.UseWell(well, null);

        bucket.IsEmpty.Should().BeFalse("has been filled");
        well.LitersRemaining.Should().BeApproximately(WellInitialFillLevel - BucketSize,
            double.Epsilon, "well level has been reduced by bucket amount");
    }

    [Fact]
    public void UseWell_NoBucket()
    {
        const double WellInitialFillLevel = 20D;
        
        var well = new Well(WellInitialFillLevel, default(double));
        var person = new Person();
        
        person.UseWell(well, null);

        well.LitersRemaining.Should().Be(WellInitialFillLevel, "unchanged");
    }

    [Fact]
    public void UseWell_AdditionalBucket()
    {
        const double WellInitialFillLevel = 20D;
        const double BucketSize = 1.86D;
        
        var well = new Well(WellInitialFillLevel, default(double));
        var bucket = new Bucket(BucketSize);
        var person = new Person();
        
        person.UseWell(well, bucket);
        
        bucket.IsEmpty.Should().BeFalse("has been filled");
        well.LitersRemaining.Should().BeApproximately(WellInitialFillLevel - BucketSize,
            double.Epsilon, "well level has been reduced by bucket amount");
    }

    [Fact]
    public void MoveBucket_Forward_Simple()
    {
        var (first, second) = CreateMinimalChain();
        var bucket = CreateFilledBucket(1.2D);
        SetBucket(first, bucket, true);

        HasBucket(first, true).Should().BeTrue();
        HasBucket(second, true).Should().BeFalse();
        first.MoveBucket(1)
            .Should().BeTrue("successfully moved forward to next person");
        HasBucket(first, true).Should().BeFalse("sent forward");
        HasBucket(second, true).Should().BeTrue("received");
        HasBucket(first, false).Should().BeFalse();
        HasBucket(second, false).Should().BeFalse();
    }
    
    [Fact]
    public void MoveBucket_Backward_Simple()
    {
        var (first, second) = CreateMinimalChain();
        var bucket = new Bucket(1.2D);
        SetBucket(second, bucket, false);

        HasBucket(first, true).Should().BeFalse();
        HasBucket(second, true).Should().BeFalse();
        HasBucket(second, false).Should().BeTrue();
        first.MoveBucket(1)
            .Should().BeTrue("successfully moved backward from next person");
        HasBucket(first, true).Should().BeFalse();
        HasBucket(second, true).Should().BeFalse();
        HasBucket(first, false).Should().BeTrue("received");
        HasBucket(second, false).Should().BeFalse("sent backward");
    }
    
    [Fact]
    public void MoveBucket_Forward_And_Backward()
    {
        var (first, second) = CreateMinimalChain();
        var bucket = CreateFilledBucket(1.2D);
        var backwardBucket = new Bucket(1.2D);
        SetBucket(first, bucket, true);
        SetBucket(second, backwardBucket, false);

        HasBucket(first, true).Should().BeTrue();
        HasBucket(second, true).Should().BeFalse();
        HasBucket(first, false).Should().BeFalse();
        HasBucket(second, false).Should().BeTrue();
        first.MoveBucket(1)
            .Should().BeTrue("successfully moved forward to and backward from next person");
        HasBucket(first, true).Should().BeFalse("sent forward");
        HasBucket(second, true).Should().BeTrue("received");
        HasBucket(first, false).Should().BeTrue("received");
        HasBucket(second, false).Should().BeFalse("sent backward");
    }
    
    [Fact]
    public void MoveBucket_NoBuckets()
    {
        var (first, second) = CreateMinimalChain();

        HasBucket(first, true).Should().BeFalse();
        HasBucket(second, true).Should().BeFalse();
        HasBucket(first, false).Should().BeFalse();
        HasBucket(second, false).Should().BeFalse();
        first.MoveBucket(1)
            .Should().BeTrue("nothing was moved, but there was no error either");
        HasBucket(first, true).Should().BeFalse();
        HasBucket(second, true).Should().BeFalse();
        HasBucket(first, false).Should().BeFalse();
        HasBucket(second, false).Should().BeFalse();
    }
    
    [Fact]
    public void MoveBucket_ForwardBlocked()
    {
        var (first, second) = CreateMinimalChain();
        var bucket1 = CreateFilledBucket(1.2D);
        var bucket2 = CreateFilledBucket(1.2D);
        SetBucket(first, bucket1, true);
        SetBucket(second, bucket2, true);

        HasBucket(first, true).Should().BeTrue();
        HasBucket(second, true).Should().BeTrue();
        first.MoveBucket(1)
            .Should().BeTrue("nothing was moved, but there was no error either");
        HasBucket(first, true).Should().BeTrue();
        HasBucket(second, true).Should().BeTrue();
    }
    
    [Fact]
    public void MoveBucket_BackwardBlocked()
    {
        var (first, second) = CreateMinimalChain();
        var bucket1 = CreateFilledBucket(1.2D);
        var bucket2 = CreateFilledBucket(1.2D);
        SetBucket(first, bucket1, false);
        SetBucket(second, bucket2, false);

        HasBucket(first, false).Should().BeTrue();
        HasBucket(second, false).Should().BeTrue();
        first.MoveBucket(1)
            .Should().BeTrue("nothing was moved, but there was no error either");
        HasBucket(first, false).Should().BeTrue();
        HasBucket(second, false).Should().BeTrue();
    }

    [Fact]
    public void MoveBucket_AlreadyPerformedInStep_Simple()
    {
        const int Step = 12;
        
        var person = new Person();
        SetLastStepPerformed(person, Step);

        person.MoveBucket(Step)
            .Should().BeFalse("already performed in this step");
    }
    
    [Fact]
    public void MoveBucket_AlreadyPerformedInStep_Complex()
    {
        const int Step = 12;
        
        var (first, second) = CreateMinimalChain();
        var third = new Person();
        third.JoinChain(second, true);
        SetBucket(first, CreateFilledBucket(1.2D), true);

        first.MoveBucket(Step)
            .Should().BeTrue("can move");
        second.MoveBucket(Step)
            .Should().BeFalse("already performed in this step");
    }
    
    [Fact]
    public void MoveBucket_NoNeighbor()
    {
        var person = new Person();
        SetBucket(person, CreateFilledBucket(1.2D), true);
        
        person.MoveBucket(1)
            .Should().BeFalse("no right neighbor to move to/from");
    }

    [Theory]
    [MemberData(nameof(StringRepresentationData))]
    public void StringRepresentation(Person person, string expected, string reason)
    {
        person.ToString()
            .Should().Be(expected, reason);
    }

    public static TheoryData<Person, string, string> StringRepresentationData()
    {
        return new()
        {
            {
                CreatePerson(null),
                "🫲",
                "has no bucket"
            },
            {
                CreatePerson(false),
                "🔘",
                "has empty forward bucket only"
            },
            {
                CreatePerson(false, false),
                "🔘",
                "has empty backward bucket only"
            },
            {
                CreatePerson(true),
                "🔵",
                "has full forward bucket only"
            },
            {
                CreatePerson(true, false),
                "🔵",
                "has full backward bucket only"
            },
            {
                CreatePerson(false, 
                    then: p => SetBucket(p, CreateFilledBucket(1), false)),
                "🔘",
                "has empty forward bucket and full backward bucket"
            },
            {
                CreatePerson(true, 
                    then: p => SetBucket(p, new Bucket(1D), false)),
                "🔵",
                "has full forward bucket and empty backward bucket"
            }
        };

        static Person CreatePerson(bool? bucketFull, bool forwardBucket = true, Action<Person>? then = null)
        {
            var person = new Person();
            if (bucketFull == null)
            {
                return person;
            }

            var bucket = bucketFull.Value ? CreateFilledBucket(1D) : new Bucket(1D);
            SetBucket(person, bucket, forwardBucket);
            then?.Invoke(person);

            return person;
        }
    }

    private static (Person FirstPerson, Person SecondPerson) CreateMinimalChain()
    {
        var firstPerson = new Person();
        var secondPerson = new Person();

        secondPerson.JoinChain(firstPerson, true);

        return (firstPerson, secondPerson);
    }
    
    private static Bucket CreateFilledBucket(double size)
    {
        var bucket = new Bucket(size);
        bucket.Fill(size);

        return bucket;
    }

    #region Test Helper - ignore
    
    private static void SetBucket(Person person, Bucket? bucket, bool forwardBucket)
    {
        var field = GetBucketField(forwardBucket);
        field.SetValue(person, bucket);
    }

    private static bool HasBucket(Person person, bool forwardBucket)
    {
        var field = GetBucketField(forwardBucket);
        return field.GetValue(person) != null;
    }

    private static FieldInfo GetBucketField(bool forwardBucket) =>
        typeof(Person).GetField(forwardBucket ? "_forwardBucket" : "_backwardBucket", 
                                BindingFlags.Instance | BindingFlags.NonPublic)!;

    private static void SetLastStepPerformed(Person person, int step)
    {
        var prop = typeof(Person).GetProperty("LastStepPerformed", 
            BindingFlags.Instance | BindingFlags.Public);
        prop!.SetValue(person, step);
    }

    #endregion
}